Method for making flexible insulated wire



Oct. 6, 1931. H, DE 3. RICE 1,826,092

'IETHOD FOR MAKING FLEXIBLE INSULATED WIRE Filed Oct. 23, 1926 IAfVENTOR Harold Delilous 1211c A TTORNE Y 40 of the smaller stranded wires, or with a ti Patented Oct. 6, 1931 UNITED STATES PATENT OFFICE HAROLD DE BLOIS RICE, OF BRISTOL, RHODE ISLAND, ASSIGNOR TO NATIONAL INDIA RUBBER COMPANY, OF BRISTOL, RHODE ISLAND, A CORPORATION OF RHODE ISLAND METHOD FOR MAKING FLEXIBLE INSULATED WIRE Application filed October 23, 1926.

This invention relates to a simple and eificicnt method for making insulated electrical conductors, and particularly flexible conductors generally known as fixture wire, lamp cord and the like. The primary object of the invention is to provide a strong, pliable, i1u isture-repcllant, fibrous insulation. Another object is to provide a flexible insulated wire having a greater insulation resistance and voltage capacity than are obtained from many of the existing types of flexible wires. A further object is to provide a method for obtaining a uniform insulation by a commercially applicable, inexpensive, continuous 1 process. A further object is to supply a rubber paper insulation to flexible conductors, either single or stranded.

Electrical conductors have been wrapped with paper strips, but only in the preparation of the larger cables used for underground power distribution, and it is also necessary to enclose these paper wrapped cables in a lead sheath. In the manufacture of these heavy cables, it is-the practice to wra p the conductor with strips of paper and then to dry the wrapped conductor thoroughly and impregnate the paper with varnishes, oils, waxes, tars, pitches, and'the like. The purpose of the impregnation is to supply 80 a suitable insulating value, for satisfactory as fixture wire, etc.

According to the present practice of manufacturing flexible electric wiring, a copper conductor, either single or stranded, is first covered with a serving of yarn, in the case plating Where the single wires are of ap preciable size. In the latter instance tinned copper wires may also be stranded, in which case no further protection is necessary. The

reason for this preliminary wrapping or plating is to prevent the migration of sulphur or other ingredients in the rubber insulation which is thereafter applied. Sulphur is known to migrate through the rub ber insulation and, when it comes in contact Serial No. 143,791.

with the copper, sets up a reaction therewith forming a copper sulphide which has no insulating value but actually tends to cause short circuits. After the preliminary treatment to prevent migration of sulphur, the wire is then covered with rubber by one of two methods. In the first method, the wire is run through a tubing machine and there covered with a seamless rubber insulation. In the other method, the rubber insulation is calcndercd into sheets, out into strips, and the strips wrapped about the wire. In the latter method it is diiiicult to obtain a uniform thickness of insulation around the conductor on account of the lap joint. When the insulation has been applied by the tubing method, the covered wire is passed through soapstone and coiled intoa pan and liberally coated with soapstone. The pan is placed in a vulcanizer and given the required heating, after which the wire is unpanned, i. e., removed from the pan, and cleaned. \Vit-h the stripping method of applying the rubber insulation, panning is not employed. After vulcanization in both instances the wire is reeled up preparatory to braiding the jacket over the insulation.

\Vith some of the wire made according to the above standard practice, the rubber insulation is so thin that it may be easily ruptured. VVheu the insulation is ruptured or cut the cotton wrapping on the bare conductor is exposed to moisture and actually functions as a wick thereby causing short circuits. This, of course, does not occur when the wire has been tinned. With stranded wires, whether tinned or not, it is generally the practice to wrap a serving of yarn about the conductors in order to prevent loosened broken ends from piercing the layer of rub ber insulation.

Vith a particular embodiment in mind but without intention to limit the invention beyond what may be required by the prior art,

the invention comprises applying strips of insulating fibrous material directly to an electrical conductor, and thereafter applying a coating and protective covering. 'More specifically, the invention consists in Wrapping a rubber-containing insulating paper about an electrical conductor, covering the paper wrapping with a substantially continuous layer of rubber, and covering the coating with a fibrous protecting jacket.

In the drawings are shown various embodiments of the invention. Fig. 1 shows a stranded conductor 1 with wrappings of the rubber containing paper 2 and 8 wound in the same direction and at approximately the same angle. the strip 3 breaking joints with the strip A coating of rubber derived from rubber latex is indicated at 4. In Fig. 2 a solid conductor 1 is wrapped with two strips of paper 2 and 3, the second strip 3 being laid at a dififerent angle, but in the same direction as 2. l represents a layer of rubher. In Fig. 3 a stranded conductor 1 is insulated with strips of paper 2 and 3 applied to the conductor in opposite directions, and the whole covered with a rubber layer at. Fig. a shows a solid conductor 1 covered with two wrappings of latex paper insulation 2 and 3 and a braided jacket 5 over the insulated wire. In Fig. 5 the construction is similar to that shown in Fig. 4 except that a rubber layer 4 is located between the outer winding of paper 3 and the braided jacket 5. In Fig. 6 two conductors 1 insulated with wrappings of latex paper 2 and 3 are laid parallel to each other, or twisted, and a yarn or other filling 6 placed to smooth over the irregularities caused by the twists in the conductors l or to fill the hollows if the conductors be laid side by side, and a rubber insulating or protecting layer t is located on the outside of the wrapped wires and yarn filling.

In one illustration of the invention. the electrical conductor consists of stranded bate copper wires. The conductor is then passed through a wrapping machine where a strip of insulating paper is applied at a suitable angle. e. 92, 60, corresponding with three wraps to the inch w'th a A strip. lVithout interruptingthe progress of the wire, a second serving of the insulating paper strip is applied over the first, but at a different angle, corresponding with two wraps per inch, and oppositely disposed. \Vith two wraps, at the angle above indicated, the joints or laps in the first serving of paper will be broken by the second serving, thus insuring no exposure of the conductor when the wire is flexed.

The wrapped wire, with no further treatment, may be used at this point of manufacture for a number of purposes. However, the ordinary fixture wire is covered with a braided jacket. Prior to the application of the braided jacket, the paper insulated wire maybe passed through a bath of coating composition. preferably a rubber dispersion. one example of which is rubber latex. This coating. when dry. gives a continuous layer of rubber over the servings of paper. A suitable jacket of fibrous cover is then applied over the coatin naeaoea la the above illustration a stranded conductor has been used. The invention may be carried out with equal facility with a solid conductor. The wrappings of insulating paper may be applied at diti'erent angles in the same direction or oppositely disposed and the successive operations may be lapped or abutted. as desired. In any case. it is preferable for most purposes to apply two layers of the insulating paper at different angles, so that the joints of the outer layer will not correspond with the joints or laps of the inner layer. This insures a continuous unbroken insulation.

The insulating fibrous material employed in the invention is what is known as rubber latex paper lt has been generally recognized that paper would be splendid insulating material in itself if it could be made so that minute apertures between the fibers could be eliminated. This. however, has not been accomplished except in parchmentized papers, which are far too expensive and too brittle for use as insulation on the smaller wires. With the advent of latex paper. and particularlv the manner in which it is made. it has now become possible to utilize paper as an insulator. Generally speaking. the paper is manufactured somewhat follows: A quantity of latex is added to the heater. and the rubber is coagulated upon the beaten pulp by the addition of a suitable coagulant. The pulp is then manufactured into paper in the usual-way. hen so prepared, the paper is highly flexible, water repellant, elastic and possesses great strength and durability. The presence of the rubber dispersed throughout the paper and substantially surrounding the fibers in the sheet, makes it possible to fill uptheminnte interstices through which current leakage would ordinarily take place, and thereby the insulating value of the paper is greatly increased. By suitable control of the proportion of rubber in the final product, the insulating value can be brought to a figure considerably in excess of the dielectric strength of the best papers obtainable. Pre-- sumably the same dielectric strength might be reached with a carefully prepared thick paper contained no rubber. but this product could not then be wound and it would be far too stiff for practical service.

For the purpose of the present invention, the term latex paper as herein employed is understood to include fibrous sheets containing rubber derived from natural latex or from artificial dispersions of rubber. The term latex paper is also to he understood as including the presence of filling materials, water-proofing substances and other special ingredients, such as oils, waxes. pitches, asphalts. etc. Preferably these materials are incorporated with the pulp prior to the manufacture of the paper.

Nowhere in the art has reliance been placed upon paper as a sole insulating means. At the present time practically the only use of paper insulation is in the manufacture of lead covered cables, in which the paper wrapping is impregnated with avarnish or other insulating compound. It has not been possible to wind a smooth layer of paper insulation on conductors of small diameter, for the reason that the papers hitherto known have lacked sufiicient elasticity to eliminate the tendency to Wrinkle. Elasticity is a prominent and important characteristic of the latex paper insulation used-in the present invention. By the use of such paper the windings may be applied smoothly, rapidly and without wrinkles, which has been impracticable in the prior art, even with the best types of papers.

The coating of rubber over the outside wrapping is preferably derived from a dispersion of rubber. either artificial or natural,

and with or withoutrompounding ingredients. coloring materials, fireproofing ingredients. etc. The purpose of the covering or seal of rubber over the wrappings is to supply an additional binder for the wrapping. particularly to hold; the wrappings in place when splices are made. The coating being a continuous layer of pure or very high-grade rubber. it will be apparent that the tensile strength and stretch in the coating are far greater than are required. The rubber coating servesalso to maintain a continuous, even. smooth insulation throughout the entire life of the cord.

For some purposes, the rubber coating may be omitted. or another coating. such as a shellac, wax. oil, etc., may be used. If so desired. a sealing coat maybe applied between the successive wraps of latex paper. A fireproof coating or jacket may be laid over the insulated wire,-as for instance a braided jacket of asbestos fibre. It is within the scope of the invention to incorporate with the coating composition fireproofingmaterials. waterproofing materials and other ingredients for special purposes.

For example, a number of coatings may be applied in. any suitable fashion to the surface of the outside wrap of paper. and the coatings may contain a color. In this phase of the invention. it is understood of course that a braided jacket or other protective layer is unnecessary. A serving'of yarn or other fiber, or a braided cover, may be placed between the paper wraps as well as over the outer wrap, with or without the above coating compositions. Other modifications and arrangements may also be made without departing from the spirit of the invention. Two or more conductors, insulated as above described, may be twisted together or otherwise assembled and covered with a suitable conductors, is eliminated. With the larger conductors, the tin plating is rendered unnecessary although plating may be used if required to meet various specifications of the trade. Since the coating or seal is applied by a dipping operation, it is possible to eliminate the expensive machinery now required for the preparation of rubber insulating compounds and the application of these to the wire. The process of the present invention is practica ly continuous and, furthermore, may be carried out from the bare wire to the finished roduct, in a single machine. In fact, by a suitable arrangement of the various machines, the wire making process may be made practically continuous from the stranding operation to the final packaging for sale. Furthermore, the process may be carried out at considerable speed, e. g., in excess of 25 linear ft. er minute.

Having thus describe my invention, what I claim as new and useful and desire to secure by Letters Patent, is:

An electrical cable comprising a core of electrical conducting material, insulating material composed of latex paper spirally wrapped around the conducting material, and, a covering of an in-situ deposit of the solids of an aqueous dispersion of rubber over the latex paper.

Si ned at Bristol, in the county of Bristol, and tate of Rhode Island, this 20th day of October, 1926.

HAROLD on BLOIS RICE. 

